中文题名: | 基于数据驱动的舰载直升机非定常流场与飞行安全边界研究 |
姓名: | |
学号: | BX2001326 |
保密级别: | 公开 |
论文语种: | chi |
学科代码: | 082501 |
学科名称: | 工学 - 航空宇航科学与技术 - 飞行器设计 |
学生类型: | 博士 |
学位: | 工学博士 |
入学年份: | 2020 |
学校: | 南京航空航天大学 |
院系: | |
专业: | |
研究方向: | 直升机空气动力学 |
第一导师姓名: | |
第一导师单位: | |
完成日期: | 2024-10-20 |
答辩日期: | 2024-12-04 |
工作时间: | 2024-12-20 |
外文题名: |
Data-Driven Research on Unsteady Flow Field and Ship-Helicopter Operating Limits of Shipboard Helicopters |
中文关键词: | |
外文关键词: | helicopter ; ship airwake ; dynamic interface ; data-driven ; multi-task learning ; reduced order model ; ship-helicopter operating limits |
中文摘要: |
舰载直升机在起降和飞行过程中需要面对极为复杂的气动环境,这种环境具有高度的非定常性和不确定性,给直升机的飞行安全带来了巨大的挑战, 但现有的研究手段存在流场数据量大、数值计算成本高等问题。且近年来,深度学习、降阶模型等数据驱动方法在空气动力学等工程应用领域的研究开始逐渐深入。鉴于此,本文首先提出了具有拓展性的多任务学习网络MT-Swin-T,实现了旋翼翼型流场与升力系数的联合预测。其次,分别通过POD-RBF和POD-MLP模型预测旋翼非定常气动力数据,展示了降阶模型在提升计算效率方面的优势。接着还通过POD、SPOD方法对舰艉流场的空间和时频特性进行了降阶分析,提出了基于AE-RBF和PODAE-RBF的舰艉流场预测模型,能够在不同工况下准确预测舰艉流场特征。并基于 POD 和 SPOD 降阶模型,建立了直升机非定常载荷滤波方法,研究保留模态数和不同频率成分对直升机非定常载荷水平的影响。此外,结合降阶预测模型,提出了连续性风限图计算方法,并分析了不同着舰方式对着舰飞行安全边界的影响。主要工作内容包括以下几个方面: (1) 本文提出了一种多任务深度学习框架MT-Swin-T,结合Swin-Transformer和MLP网络,实现了旋翼翼型的多任务学习和流场预测。MT-Swin-T通过硬参数共享的方式,针对不同任务使用不同的输出结构,即共享Swin-Transformer的编码器部分学习翼型的形状和初始条件的特性,解码器则负责预测速度场信息,同时使用MLP预测升力系数。研究通过实验分析了数据集规模、模型参数、不同损失函数组合等因素对模型精度的影响。实验表明,较大规模的数据集和匹配的模型参数能够显著提升模型的收敛效率与预测精度。相较于传统CFD模拟方法,MT-Swin-T不仅缩短了计算时间,还能在多任务的情况下提供更加准确的预测结果。 (2) 第三章利用POD方法对AH-1G旋翼的非定常气动力数据进行了降阶处理,提取了主要模态,并提出了POD-RBF和POD-MLP两种降阶预测模型。这两种模型分别使用径向基函数方法和多层感知机对测试集中样本的POD模态系数进行预测,并重构出完整的气动力数据。实验表明,POD-RBF模型在载荷波动较大的区域表现出较好的误差控制,而POD-MLP模型在更复杂的飞行工况下误差较大,泛化能力相对较弱。 (3) 针对非定常舰艉流场提出了多种降阶预测模型。首先利用高精度DES方法计算出舰艉非定常流场数据,然后分别采用上一章发展的POD方法和SPOD方法对流场数据进行降阶,对不同风向角条件下艉流场能量特性与频率特性进行了分析。并研究发展了AE-RBF模型,用于时均舰艉流场的降阶预测。此外,还结合POD与自编码器建立了PODAE-RBF模型,用于非定常舰艉流场的降阶预测。结果表明,AE-RBF和PODAE-RBF模型能够在不同风向角和来流风速下准确预测流场特性,且随着潜变量维度的增加,预测效果进一步提升。 (4) 在直升机/舰船动态界面的分析中,本文采用了POD数据降阶传递方法和SPOD非定常载荷滤波方法。POD数据降阶方法通过选取少数主要模态,有效表达舰艉流场的时均特性,大幅降低了流场数据规模,并能够准确模拟直升机着舰进场过程中操纵杆量的变化。SPOD方法则用于分离出不同频率下的模态特征,能够有效捕捉直升机非定常载荷中的低频能量分布。通过保留0.2-3Hz频率成分的SPOD重构流场数据,研究实现了对直升机非定常载荷水平的准确预测。 (5) 本文结合直升机平衡特性的理论风限图计算方法,以及第四章提出的舰艉流场降阶预测模型,发展出了一套新的基于降阶模型的连续性风限图计算方法。此方法通过降阶预测模型ShipROM实时获取时均舰艉流场,极大提高了计算效率,省去了传统CFD方法中多次重新计算舰艉流场的步骤。研究还分析了不同着舰路径对飞行安全边界的影响,结果表明,从甲板后方进场时的飞行安全边界较大,尤其是直升机机头迎风进场时安全性最高,而侧向进场时,尤其是右舷侧进场,尾桨受侧洗速度影响较大,飞行员操纵负荷增加,飞行安全边界相对较小。 |
外文摘要: |
Shipboard helicopters encounter extremely complex aerodynamic environments during take-off, landing, and flight, characterized by high levels of unsteadiness and uncertainty, which pose significant challenges to flight safety.However, the existing research methods have some problems, such as large amount of flow field data and high cost of numerical calculation. In recent years, data-driven methods such as deep learning and reduced-order models have gradually gained traction in fields like aerodynamics. In light of this, this thesis first proposes an extensible multi-task learning network, MT-Swin-T, which achieves joint prediction of rotor airfoil flow fields and lift coefficients. Then, POD-RBF and POD-MLP models are employed to predict the unsteady aerodynamic forces of the helicopter rotor, demonstrating the advantages of reduced-order models in improving computational efficiency. Additionally, the spatial and spatio-temporal characteristics of the ship airwake are analyzed with POD and SPOD methods, and AE-RBF and PODAE-RBF-based prediction models are proposed to accurately predict ship airwake characteristics under various innitial conditions. Based on the POD and SPOD reduced-order models, a filtering method for unsteady helicopter loads is developed, examining the influence of retained modes and different frequency components of airwake on unsteady helicopter load levels. Furthermore, a continuous SHOL(ship-helicopter operating limits) calculation method based on reduced-order prediction models is proposed, and the impact of different landing approaches on SHOL is analyzed. The main contributions include the following: (1) This investigation proposes a multi-task deep learning framework, MT-Swin-T, which combines the Swin-Transformer and MLP networks to achieve multi-task learning and flow field prediction for rotor airfoils. MT-Swin-T employs hard parameter sharing, where the Swin-Transformer encoder learns the airfoil's shape and initial condition features, while different output structures are used for different tasks. The decoder predicts flow velocity fields, and the MLP predicts lift coefficients. Experimental results indicate that larger datasets and matched model parameters significantly enhance convergence efficiency and prediction accuracy. Compared to traditional CFD methods, MT-Swin-T reduces computation time and provides more accurate predictions in multi-task conditions. (2) This chapter uses POD to process aerodynamic data of the AH-1G rotor, extracting primary modes, and proposes two reduced-reconstruction models: POD-RBF and POD-MLP. These models use radial basis functions and multi-layer perceptrons to predict POD modal coefficients of test samples and reconstruct complete aerodynamic data. The results show that the POD-RBF model exhibits better accuracy in regions with significant load fluctuations, while the POD-MLP model shows higher errors and limited generalization in more complex flight conditions. (3) For the unsteady ship airwake, multiple reduced-order prediction models were developed. High-fidelity DES simulations were used to simulate the unsteady airwake flow field, followed by POD and SPOD techniques to analyze energy and frequency characteristics under different wind angles. The AE-RBF model was developed for predicting time-averaged airwake flow fields, and a PODAE-RBF model was established for unsteady airwake flow fields. Results indicate that AE-RBF and PODAE-RBF models can accurately predict flow characteristics under varying wind directions and inflow velocities, with improved predictive performance as latent variable dimensions increase. (4) In the analysis of helicopter/ship dynamic interface, the investigation employs POD data reduction transmission and SPOD unsteady load filtering methods. The POD method captures the time-averaged characteristics of the ship airwake flow field using a small number of primary modes, significantly reducing the data size while accurately simulating helicopter control inputs during landing approaches. The SPOD method extracts modal characteristics across different frequencies and effectively captures low-frequency energy distribution in unsteady helicopter loads. By retaining SPOD frequency components in the 0.2-3 Hz range, the study achieves accurate predictions of unsteady helicopter load levels. (5) The analysis integrates the theoretical SHOL calculation method for helicopter trimming characteristics with the reduced-order airwake flow field prediction models from Chapter 4, developing a continuous SHOL calculation method based on reduced-order models. This method, ShipROM, obtains time-averaged ship airwake flow fields in real-time, greatly improving computational efficiency by eliminating the need for multiple re-simulations of the airwake flow field in traditional CFD methods. The study also analyzes the impact of different landing paths on SHOL, showing that rear-deck landing approaches have larger safety boundaries, especially when the helicopter nose is facing into the wind. In contrast, sideward approaches, particularly on the starboard side, reduce safety boundaries due to increased pilot workload from tail rotor sidewash effects. |
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中图分类号: | V211.52 |
馆藏号: | 2024-001-0529 |
开放日期: | 2025-06-03 |